RED BLUFF, Calif. -

Police swarmed the campus at Red Bluff High School Monday, but don't be alarmed, it was only a drill.

Several law enforcement agencies participated in an active shooter drill on Monday.

It ran from 8:30 a.m. to 1:30 pm. The purpose of the exercise was to provide officers with training in a simulated critical incident environment. Among the organizations participating were Red Bluff Police, Corning Police and the Tehama County Sheriff's Office.

School was not in session Monday and no students were allowed on campus during the exercise.

The process involved someone acting like an active shooter. Red Bluff Police Captain Kyle Sanders said even though real ammunition is not used, the training can still be dangerous.

"While we are not using real ammunition, we are using sim-unition – it is ammunition that will work in a fire arm but it shoots out kind of like a paintball and people could get hurt," Capt. Sanders said.